The subject matter of the present invention is a simple chemical process for the rapid racemization of optically active N-acylamino acids which are in aqueous solution.
The preparation of L-amino acids corresponding in configuration to the naturally occurring amino acids from synthetic amino acid racemates can be accomplished by selectively deacylating the N-acyl-L isomers by the action of N-acyl-L-amino acid amidohydrolases (called "acylases" for brevity). The aqueous cleavage solutions contain, after the separation of the target product, i.e., the L-amino acid, the enzymatically uncleaved L-acyl-D form. This has to be racemized so that it can be returned to the enzymatic cleavage process and again yield L-amino acids after the asymmetrical hydrolysis of the N-acyl-L content. In this manner it becomes possible to transform all of the racemic amino acid to the desired L form.
The known methods for the racemization of optically active N-acyl amino acids have serious disadvantages. The racemization of optically active N-acyl amino acids in the melt is accompanied by decomposition by high temperatures and long action times. Also, the process would be applicable to the dilute aqueous solutions resulting from the enzymatic cleavage of the N-acyl-L form, only after the difficult separation and refinement of the N-acyl-D compound, if it were possible to avoid thermal decomposition. The racemization of optically active N-acyl amino acids in special organic solvents requires the concentration of the amino acid solution, acidification with mineral acid, extraction with the solvent, and heating in the solvent to more than 160.degree. C., and then the removal of the solvents, and therefore it is too complicated and expensive. The racemization of N-acetyl amino acids in aqueous solutions with acetic anhydride requires long reaction times and large amounts of anhydride and caustic soda solution.